What is the difference between steel casing pipe and carrier pipe?

Although steel casing pipe and carrier pipe are similar in name, they are different in structure and function.

Casing Pipe:
Casing pipe is equipment used for oil well drilling and belongs to OCTG (Oil Country Tubular Goods) pipes. It usually has thicker walls that are used to withstand pressure and maintain the stability of the well wall. At the same time, cement can also be used to fill the annular space between the casing and the well wall. Casing helps isolate different geological layers, prevent fluids from different formations from mixing with each other, and ensure the purity of oil and gas resources. The industrial and international standards for oil casing include API SPEC 5CT, etc. In order to ensure performance and quality, oil casing usually uses carbon steel and stainless steel as raw materials.

Carrier Pipe: 

Carrier pipes are mainly used to transport liquids such as water and oil. They are common pipe equipment in municipal water supply and irrigation systems. Unlike tubing, carrier pipes can be widely used in ground or underground fluid systems, but tubing is mainly used for the transportation of oil.

The main function of the carrier pipe is to transport fluid from one place to another. Depending on the purpose, pipes can be made of different materials, such as steel pipes, copper pipes, cast iron pipes, titanium alloy pipes, etc. Pipes are mostly long and connected.

Casing Pipe vs Carrier Pipe:

Simply put, there are differences in structure and function between casings and carrier pipes: casings, as part of the wellbore, play a supporting and protective role without withstanding internal fluid pressure; carrier pipes are the pipes that actually transport fluids and are Placed inside the casing and withstand the pressure of the internal fluid. This configuration allows for safer and more efficient fluid transfer while protecting the wellbore from damage.

Steel Casing Pipe vs Carrier Pipe Size

Carrier pipe:

Carrier pipe inside of casing under railroad Track and right of way shall be of good construction of steel, wrought iron, cast iron, pure or alloyed iron; and shall be either seamless pipe or substantially welded pipe, with welded coupling, or other "approved" joints. Pipe shall be laid with slack (no tension or compression) in the line. Use of a carrier pipe of material other than the above mentioned iron or steel must be approved by the chief engineer of the railroad.
 
Casing Pipe:
Casing pipe and joints shall be uniformly thick steel construction approved by the railroad's chief engineer and shall be capable in its entirety of withstanding load of railroad roadbed, track and traffic; also shall be constructed so as to prevent leakage of any matter from the casing or conduit throughout its length under track and railroad right of way.

The casing shall be installed with even bearing throughout its length, and to prevent formation of standing liquids shall slope to one end.

Wall thickness of the casing must be no less than that specified in the attached steel casing pipe wall thickness chart.
Inside diameter of the casing shall be at least 10% larger than the outside diameter of the carrier pipe but no less than 2 inches greater than largest outside diameter of carrier pipe, joints or couplings.

The specific differences are shown in the table below:

Feature	Casing Pipe	Carrier Pipe
Primary Function	To provide structural support to the wellbore and prevent collapse.	To transport fluids (such as oil, gas, or water) within the wellbore.
Pressure Containment	Does not contain pressure; it is vented.	Designed to contain the pressure of the fluid being transported.
Material	Typically made of steel or other strong, durable materials.	Can be made of steel, PVC, HDPE, or other materials suitable for fluid transport.
Wall Thickness	Generally thicker to withstand geological stresses without buckling.	Thinner compared to casing pipe since they are designed to contain fluid pressure, not geological stresses.
Diameter	Larger diameter to encompass the wellbore and any internal pipes.	Smaller diameter; its size is determined by the required flow capacity for the fluid.
Design	May have perforations or slots for specific applications like filtering or venting.	Designed for efficient fluid flow with minimal resistance and friction.
Standards	Adheres to standards like API SPEC 5CT for oil and gas applications.	May follow different standards depending on the material and application, such as ASTM for PVC pipes.
Installation	Installed first and then cemented into place.	Installed within the casing pipe after the casing is in place.
Maintenance	Generally requires less maintenance due to its structural role.	May require more frequent inspection and maintenance due to contact with the transported fluid.
Applications	Used in oil and gas wells, water wells, and other types of boreholes.	Used for the actual conveyance of fluids in various industrial, municipal, and agricultural applications.

Read more: What are the steel grades of OCTG casing? or Casing Pipe and Drill Pipe